This section provides background information related to the present disclosure which is not necessarily prior art.
Cultivation of photosynthetic terrestrial and aquatic plants is a major economic activity throughout the world and provides most people with the majority of their caloric requirements. In addition to agricultural production, many types of photosynthetic terrestrial and aquatic plants, such as flowers, are produced for other uses. Cultivation of these photosynthetic species is often complicated by plant diseases and disorders, which can significantly reduce the productivity of farms. Damage during harvest of crops (e.g., wounds on fruit or tubers) is another time at which disease or disease-causing organisms can negatively impact producers. As a result, farmers use a variety of methods to limit plant disorders and diseases, including chemical treatments, which involve added costs and the potential to damage the environmental, local biodiversity, and the health of farmers and other humans consuming or interacting with the agricultural products. These chemical treatments as well as genetic engineering are widely used to improve the ability of a plant to resist disease and as treatment for a disease, but an over-dependence upon these chemical treatments in modern agriculture has led to widespread resistance and led to a desire for more natural ways to promote healthy immune function in plants.
A plant disorder may be defined as any abnormal plant growth or development. Affected plants do not live up to a grower's normal expectations and are incapable of carrying out normal physiological functions to the best of their genetic potential. Biotic disorders are more typically called plant disease's and are caused by infectious organisms. Some of the most common plant diseases are caused by fungi, bacteria, phytoplasmas, viruses and viroids, nematodes, and parasitic higher plants.
In order for a disease to occur, the host plant must be susceptible to the pathogen or disease organism. Plants and harvested plant material may be susceptible to attack at numerous locations, including the roots, leaves, flowers or the vascular system. In many cases, the host plant must be at a certain physiological state for disease to occur. For example, some pathogenic organisms attack only young plants, others attack mature or aging plants, and some organisms can attack the plant at any growth stage. In most cases, pathogens take advantage of plants that are stressed and have weakened immune systems. Plants are exposed to many stressors that have been shown to affect health, growth, mortality, immune system health, and overall wellbeing of the plant. Sources of stress can be both biotic, such as crowding, disease, and pests, and abiotic, such as temperature extremes, weather extremes, moisture extremes, light extremes, nutrient extremes, poor soil (e.g., acidity or alkalinity, salt), pesticide toxicity, air pollution, etc.
In general, the term immunity may be defined as the ability of an organism to withstand microbial infection or disease. Plants lack an adaptive immune system like most vertebrates, but have an active innate immune system that is based on the recognition of pathogen-associated molecular patterns (PAMPs). These are conserved molecules that are unique to certain classes of microorganisms. For example, lipopolysaccharides (LPS) derived from Gram-negative bacteria, peptidoglycans from both Gram-positive and gram-negative bacteria, eubacterial flagellin, unmethylated bacterial DNA fragments, as well as fungal cell wall-derived glucans, chitins, mannans and proteins are all capable of triggering the innate immune response. PAMPs are recognized at the plant cell surface through pattern-recognition receptors (PRRs) that trigger numerous responses, some of which can help the plant diminish the effects of disease or microbial invasions.
Although the term PAMPs is used broadly to describe compounds which are recognized by the immune system, PAMPS can also be derived from nonpathogenic or non-disease causing microorganisms. When a PAMP that is nonpathogenic comes into contact with a plant, the plant immune system may become activated as if it was responding to an actual threat, thereby heightening its overall immune response. This may confer greater protection to the plant if an actual disease challenge or pathogenic organism is attacking the plant simultaneously or is likely to attack soon.
Beta glucans are polysaccharides connected by beta glycosidic linkages that can be found in various organisms, such as yeast, mushrooms, kelp, fungi, cereal grains, and others. Although much research has been done on beta glucans used as human dietary supplements or as an animal feed ingredient, the use of beta glucans to promote the immune system health of plants has never been widely commercialized. Most beta glucan products used today are derived from yeast and to a lesser extent from mushrooms, which requires an expensive production process involving extraction of the beta glucan. Existing beta glucan products, as a result of how the beta glucan is produced and its chemical structure, are consequently too expensive to be used on plants. For example, in 2012 the commercial value of such beta glucans was between about 50 to about 100 USD per kg, a price that is commercially prohibitive.
One reason relating to the high cost of beta glucans, is that the beta glucans from yeast are derived from the cell wall of the organism. As such, the resulting beta glucan content of the total biomass used to produce the beta glucan is generally less than ten to fifteen percent. Moreover, the beta glucans contained in an organism's cell wall generally must undergo expensive, multistage extraction processes in order to separate the beta glucan from other cellular materials. Another concern is the chemical composition of the beta glucan. Variations in branching structure, molecular weight, source organism, and method of production and extraction can all affect the efficacy and suitability of different beta glucan products. For example, yeast-derived beta-(1,3/1,6)-glucans comprise the majority of commercial beta glucan products that are intended to stimulate immune system activity. Beta-(1,3/1,4)-glucans from oats have been demonstrated as a useful product for reducing cholesterol, and only these types of beta glucans may be labeled as such according to FDA regulations. Several organisms produce different beta glucan structures and not all beta glucans are equally effective.